The present invention relates generally to structure and operation of gas turbine engines and more particularly to a twin spool counter-rotating turbofan gas turbine engine.
Counter-rotating turbomachinery technology is a superior approach for significant improvements in the aerodynamic performance and efficiency of axial flow fans, compressors and turbines while simultaneously reducing engine size, weight and number of parts. The development of more fuel efficient, reduced weight, reduced manufacturing and maintenance cost gas turbine engines for future aircraft will require the use of counter-rotating turbomachinery technology.
The principle behind counter-rotating turbomachinery technology is to perform or extract more work per unit length of turbomachines by replacing the stationary blade rows with fluid energy transferring counter-rotors. This provides the benefit of using fewer blade rows to obtain a particular pressure ratio, in the case of a compressor, or extract an increment of mechanical work in the case of a turbine. The advantages over a conventional design are significant improvements in the aerodynamic performance and efficiency of the fan, compressor and turbine modules while simultaneously reducing the module length, weight and number of parts. These component module advantages produce a gas turbine engine that overall has reduced length, reduced weight and is less expensive to manufacture and maintain due to a reduced part count.
Another advantage counter-rotating turbomachinery technology offers over conventional turbomachinery is the high relative blade velocities present between the rotors and counter-rotors at low rotor mechanical speeds. The high relative blade velocities present between the rotors implies that the rotors do not have to rotate as fast as a conventional transonic counterpart would require to obtain high stage loadings. Therefore, the centrifugal stresses on the rotor disk of a counter-rotating configuration are significantly lower, when compared to a conventional configuration counterpart and the disk life considerably extended. This has an enormous impact on the reduction of the manufacturing and maintenance costs associated with fan, compressor and turbine modules.
While the concept of counter-rotating turbomachinery technology is not new, application of this technology has been restricted to single stage fans, turbines, propellers and propfans due to the mechanical complexity of developing a multi-stage turbomachine with dual flow path turbofan cycle capability.
The prior art demonstrates high bypass ratio counter-rotating turbofan engines (U.S. Pat. Nos. 4,790,133, 4,860,537 and 4,947,642). However, all of these concepts are triple spool configurations requiring three drive shafts. The present invention solves or substantially reduces in critical importance problems in the prior art by providing a twin spool counter-rotating turbofan gas turbine engine structure with a counter-rotating fan and booster turbocompressor that integrates the fan module with the high-pressure compressor module by integrating one or more rotating blade rows within two or more counter-rotating blade rows and an integral fan rotor utilizing only two drive shafts.
The invention may find substantial commercial and military application in propulsion systems for jet propelled aircraft as well as land and sea vehicles.
It is a principal object of the invention to provide a twin spool counter-rotating turbofan gas turbine engine structure having the fan module integrated with the high-pressure compressor module driven by a counter-rotating turbine utilizing only two drive shafts.
It is another object of the invention to provide a twin spool counter-rotating turbofan gas turbine engine structure having a counter-rotating booster turbocompressor incorporated into one of the fan blade rows.
It is yet another object of the invention to provide a twin spool counter-rotating turbofan gas turbine engine structure having a counter-rotating booster turbocompressor incorporated into the entire fan model.
These and other objects of the invention will become apparent as a detailed description of representative embodiments proceeds.
The present invention is a twin spool counter-rotating turbofan gas turbine engine having a counter-rotating fan module integrated with the high pressure compressor and driven by a counter-rotating turbine utilizing only two drive shafts. The two drive shafts are aerodynamically coupled and rotate in opposite directions relative to each other without the use of a gearbox. The integration between the fan module and high pressure compressor allows the fan blade rows to operate at the same mechanical speed of the high pressure compressor blade rows. An afterburner module may be added to the present invention to provide thrust augmentation. Although the counter-rotating power turbine is described as a two-stage turbine it could comprise a plurality of stages. One alternative incorporates a counter-rotating booster turbocompressor into one fan blade row of the fan module and another alternative further incorporates a counter-rotating booster turbocompressor into the entire fan module, which are further integrated with the high-pressure compressor utilizing only two drive shafts. The critical components, which allow the counter-rotating booster turbocompressor to be incorporated into the fan blade rows, are the shrouds, which further splits the incoming air into a core stream and a fan stream.